The actuation of automatically pivotable external elements of a vehicle, which in particular represent top elements of a convertible vehicle and tailgate or trunk covers, but which can also be made as other external parts of a vehicle such as a gas tank cover or a door element, typically takes place in practice by fluid drives in the form of hydraulic cylinders which are hinged at one end to the vehicle body and at the other end to the external elements of the vehicle to be pivoted.
In addition to the disadvantages typically inherent in hydraulic systems with respect to the temperature behavior and to the servicing effort as well as to the typically high construction space requirements, the limited flexibility with respect to the design of the path of movement of the external element of the vehicle is disadvantageous on the use of a hydraulic drive for the pivoting of an external element of a vehicle.
It is known to move a top or a top storage well cover of a convertible vehicle using an electrical drive. In this connection, linear drives are used which are designed as replacements for a hydraulic control for the corresponding use, with the linear motion generated by an electric motor being transmitted to the at least one pivotable external element of the vehicle via a suitable multi-joint mechanism. Such a drive for a pivotable external element of a vehicle is thus complex.
The aforesaid disadvantages have a particularly serious effect on the actuation of a plurality of pivotable external elements of a vehicle such as are represented, for example, by the top elements of a convertible vehicle. With convertible vehicles whose top is stored in a folded or folded together manner, and usually in a storage well in the rear sector of the vehicle, in the open state, there is the problem of realizing a top movement between its end positions with a top which is as light as possible and with simple kinematics, with a sufficient height having to be taken into account with respect to the head area of vehicle occupants, on the one hand, and with a height having to be taken into account which is as low as possible with respect to possible spatial boundaries such as a garage roof, on the other hand, in the design of the paths of movement of the cover.
The roof elements of a top are typically driven for this purpose via a top linkage which is connected to a body via a main bearing and establishes a transmission of force, hydraulically via joints as a rule, from the drive motor up to a front end of the top.
Although the movement sequences for a clamp, a top storage well cover and the top mechanism can be designed separately per se, a compulsory control via the hydraulic drive is usually provided in the top mechanism, so that the individual joints of the top linkage cannot be controlled separately.
The German patent specification DE 198 47 983 C1 describes a multi-part, lowerable vehicle top which provides the possibility of controlling a plurality of top elements independently of one another. For this purpose, a multipart, lowerable vehicle top having at least two flexurally rigid top elements, which are pivotally connected to one another and are pivotally connected to the vehicle body via at least one top element, are designed such that hinge joints are provided for the connection of the at least two flexurally rigid top elements to one another and to the vehicle body, with at least one of the hinge joints per connection being able to be driven by means of a fluid drive.
In this known solution, a conventional transmission linkage is replaced by a complex mechanism having a plurality of hydraulic drives. In addition to the required construction effort and to the requirement of a separate hydraulic pump for each hinge point to be able to control different hinge points with independent volume flows and to a correspondingly high weight of the top, the speed of the top movement is restricted by the disadvantages of a hydraulic drive inherent in the system. These disadvantages include the high temperature dependency, the restrictions in the speed regulation due to the comparatively low stiffness of hydraulic systems and their dead times as well as a poor efficiency.